Memory is one type of integrated circuitry, and is used in computer systems for storing data. Memory may be fabricated in one or more arrays of individual memory cells. Memory cells may be written to, or read from, using digit lines (which may also be referred to as bitlines, data lines, sense lines, or data/sense lines) and access lines (which may also be referred to as wordlines). The digit lines may conductively interconnect memory cells along columns of the array, and the access lines may conductively interconnect memory cells along rows of the array.
Memory cells may be volatile or non-volatile. Non-volatile memory cells can store data for extended periods of time including when the computer is turned off. Volatile memory dissipates and therefore requires being refreshed/rewritten, in many instances multiple times per second. Regardless, memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
Ferroelectric field effect transistors (FeFET) may be utilized as memory cells. Specifically, the FeFETs may have two selectable memory states corresponding to two different polarization modes of ferroelectric material within the FeFETS FeFETs. The different polarization modes may be characterized by, for example, different threshold voltages (Vt) or by different channel conductivities for a selected operating voltage. The ferroelectric polarization mode of a FeFET may remain in the absence of power (at least for a measurable duration).
One type of ferroelectric transistor is a metal-ferroelectric-metal-insulator-semiconductor (MFMIS) transistor. Such has a gate dielectric (insulator, I) between metal (M) and a semiconductor substrate (S). Such also has ferroelectric (F) material over the metal, and has a gate (typically comprising metal, M) over the ferroelectric material. In operation, an electric field across the ferroelectric material is to be used to switch the ferroelectric material from one polarization mode to another. However, it is problematically found that the gate insulator breaks down when a sufficiently high electric field is provided across the ferroelectric material to change the polarization mode.
It would be desirable to develop new ferroelectric transistors which address the above-discussed problem, and new memory array architectures utilizing such transistors. It would also be desirable to develop read/write methodologies suitable for the new memory arrays, and possibly suitable for other memory arrays.